The recording and analysis of various types of physiological signals often facilitate the diagnosis and treatment of many medical conditions. These signals can be obtained by measuring a difference in electrical potential between at least two electrodes placed at different points on or near the body. The location of these electrodes defines a recording angle that may influence the observable characteristics of the physiological signal. Because of this, as the relative locations of the electrodes change, the characteristics of the recorded physiological signals may change as well.
In order to diagnose and treat many types of medical conditions, medical professionals look for specific characteristics of physiological signals that are indicative of such conditions. This process may be complicated by changes in the characteristics of the physiological signals due to variations in the recording locations on a subject, or variations in recording quality. Such variations may be due to skin irritation, desiccation of an electrode, defoliation of the skin, etc. Patients may also need to remove and reattach electrodes for a variety of reasons, which tend to cause variations in the recording locations. As such, medical professionals acquainted with physiological signals of a specific angle from a particular subject may have difficulty analyzing the altered physiological signals in relation to the prior signals. Such difficulty can lead to a higher incidence of diagnosis and treatment mistakes.
One example of a physiological signal that is commonly recorded is an electrocardiogram (ECG). ECG recordings are important indicators used in the diagnosis and/or treatment of many cardiac abnormalities and diseases. The ECG is a graphical representation of the electrical voltage in the heart produced during a cyclical heartbeat. In present clinical practice, up to 12 leads are often employed simultaneously for ECG monitoring. One common ECG method utilizes three leads; Lead I, Lead II, and Lead III. Each lead has a negative and a positive electrode that measure electrical potentials between various points on the body. Typically, Lead I measures the electrical potential from the right arm to the left arm, Lead II measures the electrical potential from the right arm to the left leg, and Lead III measures the electrical potential from the left arm to the left leg. From this, three additional “augmented” leads, aVR, aVL, and aVF, measure electrical potentials between a point V located centrally in the chest and each of the three limb leads.
ECG leads measure the average electrical activity generated by the summation of the action potentials of the heart at a particular moment in time. For example, during normal atrial systole, the summation of the electrical activity produces an electrical vector that is directed from the sinoatrial (SA) node towards the atrioventricular (AV) node, and spreads from the right atrium to the left atrium. This directionality is a result of the location of the SA node in the right atrium. This electrical activity is represented by the P wave of the ECG.
Given the importance of ECGs and other physiological signals in the diagnosis and treatment of many medical conditions, inconsistencies in the appearance of such signals over time may impede the diagnosis and/or treatment of a subject.